1. Technical Field of the Invention
The present invention relates to a sheet feeder unit which supplies cut sheets set in a pile thereon by a feeding roller being contacted to the cut sheets from one side thereof, and particularly to a sheet feeder unit which is capable of separating cut sheets to be supplied one after another by a frictional force generated when a leading end of the cut sheet is pushed forward to contact with a friction member which is supported at one end thereof and extended toward a conveying path of the cut sheet. The present invention may be employed for feeding a plurality of piled cut sheets one by one in various appliances such as a copying machine, printer, facsimile machine, or image reading apparatus.
2. Description of Related Art
Japanese published unexamined patent application No.7-196186 discloses the like of such sheet feeder unit, which is shown in FIG. 11. The feeder unit according to this prior art has a friction member 133 rotatably supported at its lower end by a shaft 132 to be able to stand upright and tilt, and configured to be rectangular when viewed from front. Each time a feeding roller 131 is rotated round, an uppermost cut sheet 111 is pushed forward so that a whole width of a leading end of the cut sheet 111 comes into frictional contact with the friction member 133 and causes the same to back away against a rebounding force of a spring 134 as shown by phantom lines in FIG. 11. The cut sheet 111 is thereby separated from the other and prevented from being supplied one upon another.
In order to assure the separation of cut sheets from each other, the angle xcex1 made by a surface of the friction member 133 and an uppermost cut sheet 111 is set within the range of 55xc2x0 to 85xc2x0. The above mentioned published application also teaches a friction member made of an elastic sheet and fixed at its lower end with the same angular condition as described above, instead of rotatable support by the shaft 132.
The friction member of such configuration, however, requires a very fine adjustment to successfully separate the cut sheets. According to an experiment conducted by the inventors of the present invention, the rebounding force of the spring 134 toward its initial position should be set weak to prevent residual deformation of the cut sheet caused by the friction member 133. On the other hand, the rebounding force should be strong enough to increase the frictional force between the cut sheet 111 and the friction member 133 so as to ensure the separation. It is difficult to satisfy both of these contradictory conditions. Moreover, the resiliency of cut sheets varies depending on their quality and thickness, causing differences in frictional resistance even with the use of the same friction member.
Also, the friction member 133 in this prior art arrangement is disposed downstream in a feeding direction and away from a nipping position where the feeding roller 131 presses and pushes the cut sheet 111 forward. The cut sheet, when contacted against the friction member 133, is warped and separated from the other. Since the friction member 133 is distanced from the feeding roller 131 widely enough to allow the cut sheet 111 to flexibly deform therebetween, the cut sheet 111 can easily escape from the friction member 133 which is being tilted backward. This configuration helps to prevent residual deformation of the cut sheets 111 irrespective of their thickness.
Still, the sheet feeder unit of this prior art is not fully capable of stably separating cut sheets 111 and sometimes supplies the cut sheets in plural one upon another for the following reasons. Since the friction member 133 has an even surface against which the cut sheet 111 is contacted, the more the leading end of the cut sheet 111 pushes the friction member 133 and approaches a free end thereof, the more the contacting angle therebetween widens, to let the cut sheet 111 to easily slip, causing the frictional force to become less than a desired degree. The cut sheets 111 thus slip through the friction member 133 from time to time without being fully separated from each other. Although the setting of the angle between the cut sheet 111 and the friction member 133 helps to prevent such slippage to some extent, it is not enough to fully prevent faulty feeding of cut sheets, especially of a less resilient type due to their quality or thickness.
In view of the foregoing, it is a primary object of the present invention to provide a sheet feeder unit capable of successfully separating and supplying cut sheets of any type.
To accomplish the above said object, the sheet feeder unit of the present invention comprises a support member on which a pile of sheets are loaded; a feeding roller for sending out the sheets in a sheet feeding direction, which contacts to one side of the sheets piled on the support member; and a friction member being supported at one end and having a frictional force yielding portion which is capable of contacting a leading end of the cut sheets in a sheet feeding path, the frictional force yielding portion having a static friction coefficient of 1.0 to 1.5 with respect to the sheets piled on the support member.
According to the arrangement of the present invention, the leading edge of the cut sheets is contacted by a friction member with sufficient frictional force until it is passed through and off of the tip of the friction member, whereby the object of stably feeding cut sheets one by one irrespective of their type is accomplished.
Other and further objects, features and advantages of the invention will appear more fully from the following description.